Studies of ion energy and yield from argon clusters heated by intense femtosecond laser pulses

Abstract.

Using time-of-flight spectrometry, the interaction of intense femtosecond laser pulses with argon clusters has been studied by measuring the energy and yield of emitted ions. With two different supersonic nozzles, the dependence of average ion energy $\overline{E}$ on cluster size $\overline{n}$ in a large range of $\overline{n}\thickapprox 3\times 10^{3}\thicksim 3\times 10^{6}$ has been measured. The experimental results indicate that when the cluster size $\overline{n}\leq 3\times 10^{5}$, the average ion energy $\overline{E}\propto \overline{n}^{0.5},$ Coulomb explosion is the dominant expansion mechanism. Beyond this size, the average ion energy gets saturated gradually, the clusters exhibit a mixed Coulomb-hydrodynamic expansion behavior. We also find that with the increasing gas backing pressure, there is a maximum ion yield, the ion yield decreases as the gas backing pressure is further increased.